Objectives: 1) To evaluate diagnostic techniques for B. pertussis in relation to the stage of illness and to discern which techniques provide optimal recognition of B. pertussis infection. 2) To determine the reservoir of B. pertussis infection and to assess the significance of adult transmission to infants. 3) To better understand the serologic response to contact with B. pertussis, and to discern which antibodies are important for immunoprotection. A research protocol for study has been written and submitted to the clinical research committees. The research protocol for this project was approved this year, and enrollment was begun. To date, four index cases and their families have been evaluated. Nasopharyngeal specimens have been processed with routine culture medium and direct fluorescent assay. In addition, newly developed techniques have been used with the clinical specimens. These include mouse monoclonal antibodies, developed in the Laboratory of Pertussis, for the immunofluorescent assay, and serologic methods to detect pertussis-specific antibodies. On-going enrollment of index cases of pertussis and their contacts is planned to permit evaluation of the epidemiology of pertussis within a family and the community.